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Old 2nd February 2012, 10:33 AM   #2001
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Quote:
Originally Posted by nezbleu View Post
I am genuinely glad that you found the problem and fixed it, and that you have a working amp. I am also sorry that I was a bit grumpy the other night. We are all here to help, and I dare say most of us here have benefited from help freely offered by others on this forum. I know I have. If it helps I really just wanted to get you looking in the right direction and not distracted by red herrings.

Good catch, by the way, finding that solder bridge, those can be very difficult to locate.

Thanks for the kind words nezbleu. No worries for the grumpiness, I fully understand. This was my first PCB build and I went in a little arrogant thinking it would be a cake walk. I paid for not having all the right tools (light and magnifier), but I've learnt my lesson now!

I now have 2 working O2s! Woo! The old transformer that I found in the shed does seem to work, even though it only puts out 12.5 V without a load. (Mains voltage is 230 or 40 here in Germany). I thought that more than 13 V without load was required? Maybe because I'm using low volume it's fine?

For completeness I went out looking for a better transformer. I found and bought this one at the local electronics store.

TRANSFORMER F.LED LIGHT SYSTEM 20 VA | Accessories for outdoor lighting Outdoor Lighting Lighting Home & Garden | Conrad Electronic SE - Accessories for outdoor lighting

It spits out 13.5 V without load and is rated for 1.6 A. I should be able to run both of the amps from this in parallel, no? Neither is going to get near 800 mA. One amp will live on my desk and the other will be on the move, charging at the desk.
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Old 2nd February 2012, 10:53 AM   #2002
Jokener is offline Jokener  Germany
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Hey,

the data sheets on LED and halogen bulb transformers are usually worthless.
Because the lamps will be damaged or have a reduced lifetime when driven with more than 12V, the transformers usually do NOT output more than 12V.
I have been to a shop that sells and installs lights and measured literally dozens of transformers, none came above 12V without load (so they would not work WITH load for the O2).
Also, I have bought one of the Conrad units that said 13.5V and it delivered 12.5V idle (still not enough for the O2, RocketScientist himself tested it).

That is the only reason I am having the custom transformers built for my GB thread.
They are slightly more expensive than off the shelf units, but are European quality products and come complete with the matching tip for the O2...
(Other members of the first GB thread and I have looked at many alternatives, this is the one that worked best.)

Otherwise you could always run the O2 on rechargeable batteries and swap them out and charge them externally.
More of a hassle, but it works.

Best regards,
Jokener
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Old 2nd February 2012, 11:32 AM   #2003
Alexium is offline Alexium  Ukraine
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Hi Jokener! I wonder if you have already assembled O2 with non-standard parts as you've announced before. Sorry if it has already been discussed, I wasn't around lately...
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Old 2nd February 2012, 12:19 PM   #2004
Jokener is offline Jokener  Germany
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I have ordered and received the higher-grade and military-grade parts.
But I have not yet assembled the O2's because I didn't have the time.
Once the GB-orders are out the door and things are more quiet, I will get back into hardware-mode.
The fairydust-edition is also close to being ordered, but that is an order for 250€ of components.
(Don't want to order that if I'm not about to build it.)

At least the Ersa i-Con 2C that I ordered will arrive in a couple of weeks.
Then I don't have to work with the pre-war soldering iron anymore and can expect perfect solder-joints.
(Not that you would need an i-Con for that, but I needed to buy something and hate cheap quality, so I tend to go with 'overkill'.)

Best regards,
Jokener
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Old 2nd February 2012, 08:07 PM   #2005
swalter is offline swalter  Switzerland
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Hi, the i-Con 2 is a good choice, have one myself and love it! In case you need some additional tips or accessories, solder and so on let me know, I am originally from that little town in Germany where they are produced and will get them with a substancial discount ;-)

Regarding the transformers, I found some reasonably priced ones here that will match the required specs:
Steckernetzteile Wechselstrom AC / AC Adapter - Lüdeke Elekronic Elektronikhandel

made in China though but will do for me, never had any bad experience so far. I asked the shop owner about the voltage without load and requested some datashets if possible - no datasheets but measured voltage is between 1.2 and 2.5 volts higher depending on type and specified load voltage. so the 15V one should be spot on.

You'll find my order in the GB thread

And, big thanks to the RocketScientist for this little jewel!
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Old 3rd February 2012, 12:49 AM   #2006
Fiola is offline Fiola  United States
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I got my O2 up and running. I tested with my ipod touch 4g line out and AKG K701. Sounds magical. I have never heard my K701 so alive before. Thanks for this amazing little amp!
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Old 3rd February 2012, 01:04 AM   #2007
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@Fiola, you're welcome. Glad you like the O2. The K701 is a headphone that most portable amps fall well short of driving properly. So you're especially in a sweet spot to enjoy the advantages of the O2.
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Old 3rd February 2012, 03:21 AM   #2008
jmwreck is offline jmwreck  Philippines
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Quote:
Originally Posted by RocketScientist View Post
@Fiola, you're welcome. Glad you like the O2. The K701 is a headphone that most portable amps fall well short of driving properly. So you're especially in a sweet spot to enjoy the advantages of the O2.
for me, the amp is really versatile, thank you. last time I was planning to make my own PCB and layout from your design before GB was opened. I really like the way how you designed the amp. Here is my contribution:
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Last edited by jmwreck; 3rd February 2012 at 03:41 AM.
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Old 3rd February 2012, 09:00 AM   #2009
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Originally Posted by Jokener View Post
Also, I have bought one of the Conrad units that said 13.5V and it delivered 12.5V idle (still not enough for the O2, RocketScientist himself tested it).
What would be the symptoms of a transformer that isn't delivering enough voltage? So far my old transformer that gives only 12.5 V without load appears to work, although I don't have batteries installed at the moment. In fact the amp is much too loud for me unless I have the pot very low. I intend to change the gain settings. 1x gain requires simply removing the resistors?

I have another question for you guys - one that I asked Rocket Scientist once. I wanted to know whether it will give me clean gain as a preamp for my battery box power WM61a microphone. I need just enough for simple speaker measurements. He suggested that I look at devices from Alesis, Art etc., because he only has tested the O2 to +18 dB. Is it conservative to think that it won't also be reasonable at 20+dB?

I'm more inclined to build another O2 (or use my 2 piggybacked) than buy a mixer, if I can get away with it.
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Old 3rd February 2012, 11:29 AM   #2010
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This will be my first headphone amp build and thanks to RocketScientist for all the hard work designing it and also for the all the hard work Jokener has put into the group buy, putting up with not to nice comments as well.
I have a quick question, I will be building some high end wooden enclosures for this HF amp, It’s a new venture, I have several threads on aesthetics in music reproduction equipment scattered around the tinterweb. I’m looking to combine art and music reproduction and see what comes out of the melting pot, like I said it’s a new venture and still in the ideas stage. But if this Amp is anywhere near as good as people have said then I would like to use it in combination with my hand made cases. Of course I will name the HF amp the O2 and will make all the references to your site. But I will have to charge people for them. How do I stand with respect to copy right etc ? I will be marketing them as a handmade case incorporating the O2 rather than just a HF amp.
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